Racquet construction and method of making same

ABSTRACT

A racquet construction comprising a frame having an ovaloid head portion terminating in a pair of closely spaced parallel extensions which are adapted to receive a handle at the terminal ends thereof with the head portion of the frame being defined by a pair of spaced metal portions. A beam made of a resilient elastomeric material is formed between the metal portions and holds such portions in substantially parallel relation and provides the sole support for adjoining stringing extending thereacross.

United States Patent 1191 Shockley et al. 1 June 4, 1974 5 1 RACQUETCONSTRUCTION AND METHOD 3.702701 11/1972 Vaughn et al 273/73 c x OFMAKING SAME I FOREIGN PATENTS OR APPLICATIONS [751 Inventors: Gilbertshmkleyi Richard 1,260,715 4/1961 France 273/73 H both of Rlchmond,1.442.020 5/1966 France 273/73 0 237,395 7/l925 Great Britain... 273/73D [73] Ass'gnee' Cmnpany 61,721 6/1947 Norway 273/73 H 1.442.020 3/1968France 273/73 H [22] Filed: June 12, 1972 Primar Examiner-Richard C.Pinkham 21 A l. N .2 262126 y 1 pp 0 Assistant ExaminerRichard J. Apley[52] U.S. Cl. 273/73 C, 273/73 H, 273/73 K 51 1m. (:1. A63b 49/10, A63b51/00 [571 ABSTRACT Field of Search 273/73 R, 73 C, 3 73 A racquetconstruction comprising a frame having an 273/73 73 73 K ovaloid headportion terminating in a pair of closely spaced parallel extensionswhich are adapted to re- [56] References Cited ceive a handle at theterminal ends thereof with the UNITED STATES PATENTS head portion of theframe being defined by a pair of 167 051 7/1921; Robinson 273/73 HSpaced meta Portions- A beam made of a resilient 1:862581 6/1932Robinson 273/73 E elastomeric material is formed between the metal por-1,937,787 12/1933 Robinson 273/73 H tions and holds such portions insubstantially parallel 2.164.631 7/1939 Abcll 273/73 C relation andprovides the sole support for adjoining 2,969,984 l/l96l Presnick 1273/73 R stringing extending thereacross, 3,545,756 l2/197O Nash r 1273/73 D 3.690.658 9/1972 5 Claims, 11 Drawing Figures Howe 273/73 F XPATENTEDJUH 4 I874 FIG. 9

RACQUET CONSTRUCTION AND METHOD OF MAKING SAME BACKGROUND OF THEINVENTION There are numerous types of racquets in current use which areused in playing games, such as badminton, tennis, and the like, andthese racquets generally use wood or metal to define frames for theirhead portions.

It is well known that racquets made of wood tend to warp even thoughthey are stored in special clamping devices, and are comparativelydifficult to string. Racquets made of metallic materials, such as steeland aluminum, reduce some of the problems of wooden racquets; however,they may create other problems.

It has been found that an improved racquet may be made by a uniquecombination of metal and a suitable elastomeric material and byemploying not only the teachings of the racquet art but also conceptsdisclosed in US. Pat. No. 3,204,324 to Nilsen and US. Pat. No. 3,624,885to Holliday and Barker.

SUMMARY This invention provides an improved racquet construction, andmethod of making same, which may be produced with economy and overcomescertain deficiencies of wooden and metal racquets proposed heretofore.

In particular, the racquet construction comprises a frame having anovaloid head portion terminating in a pair of closely spaced parallelextensions with the head portion of the frame being defined by a pair ofspaced metal portions. A beam made of a resilient elastomeric materialis formed between the metal portions and holds such metal portions insubstantially parallel relation. The beam provides the sole support foradjoining stringing extending thereacross and has a resiliency whichcooperates with the resiliency of individual strands comprising thestringing enabling the entire area within said head portion to be usedas an effective striking surface.

Other details, uses, and advantages of this invention will becomeapparent as the following description of the exemplary embodimentsthereof presented in the accompanying drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show presentexemplary embodiments of this invention, in which FIG. 1 illustrates oneexemplary embodiment of a tennis racquet made in accordance with thisinvention;

FIG. 2 is an enlarged fragmentary view taken on the line of 2-2 of FIG.1;

FIG. 3 is a view with parts in cross section and parts broken away takenessentially on the line 3-3 of FIG. 2;

FIG. 4 is an enlarged view similar to FIG. 3 particularly illustrating,in an exaggerated manner, the action of the resilient elastomericmaterial comprising the ovaloid head portion of the tennis racquet uponstriking a tennis ball;

FIG. 5 is a fragmentary cross-sectional view taken essentially on theline 5-5 of FIG. 1;

FIG. 6 is a perspective view illustrating a bridge member comprising thetennis racquet of FIG. 1;

FIG. 7 is a schematic perspective view with parts in cross section andparts broken away illustrating an elongated channel-like metallicstructure which is used to define the frame of a racquet constructionbeing filled with a resilient elastomeric material; FIG. 8 is aschematic presentation illustrating forming of the structure of FIG. 7once filled with elastomeric material to define a racquet frameconstruction having an ovaloid head portion and a pair of closely spacedparallel extensions;

FIG. 9 is a cross-sectional view illustrating an elongated channel-likemetallic structure which has been filled with an elastomeric material ina similar manner as the elongated structure illustrated in FIG. 7 andwhich is adapted to be formed to define another exemplary embodiment ofthe racquet construction of this invention;

FIG. 10 is a cross-sectional view taken essentially on the line l0 10 ofFIG. 9; and

FIG. 11 is a view with parts in cross section and parts broken away ofthe racquet construction made utilizing the elongated structure of FIG.9;

DESCRIPTION OF ILLUSTRATED EMBODIMENTS Reference is now made to FIG. Iof the drawings which illustrates one exemplary embodiment of a racquetconstruction or racquet of this invention which is designated generallyby the reference numeral 20 and is particularly adapted for use inplaying games such as badminton, tennis, squash, or the like. Theracquet 20, which for simplicity and ease of presentation will bedescribed hereinafter as a tennis racquet, comprises a frame 21 havingan approximately oval-shaped or ovaloid head portion 22 terminating in apair of closely spaced parallel extensions 23 which are held in positionby suitable fasteners 24. A gripping handle 25 is fixed to the lower endportions of the extensions 23 and such handle is preferably providedwith a suitable covering. The handle 25 may be fixed in position usingany suitable means known in the art.

As seen in particular in FIGS. 3 and 4 of the drawings, the ovaloid headportion 22 is defined by a pair of spaced metal portions 26 and a beam30 having a peripheral outline which corresponds substantially to theoutline of the metal portions bonded in position. The beam 30 is made ofa resilient elastomeric material and provides the sole support foradjoining stringing 31 extending thereacross and defined by cooperatingstrands 32 which extend horizontally and vertically, in the showing ofFIG. 1.

The stringing 31 defines a substantially planar striking surfacefor thetennis racquet 20 and the strands 32 comprising such stringing have anormal resilient character or resiliency. As indicated above, the beam30 is made of a resilient elastomeric material and such beam has aresiliency which is determined by the crosssectional configuration anddimensions of such beam as well as the properties of the elastomericmaterial used to make the beam. Thus, the beam is made with an in-,

herent controlled resiliency which cooperates with the resiliency of thestrands 32 of the stringing 31 to assure that substantially the entirearea confined within the head portion 22 is usable as a striking surfacewhich is free of dead spots, such dead spots being common in wooden andmetal racquets proposed heretofore.

The unique action provided by the beam 30 is illustrated in anexaggerated manner in FIG. 4 of the drawings wherein it is seen thatonce the stringing 31 of racquet forcefully strikes an associated ball,the strands 32 are stretched slightly in the usual manner; however, theresilient beam 30 is also deflected from its normal solid line positionessentially to a dotted line position as illustrated at 33 in FIG. 4.

Each of the metal portions 26 comprising the exemplary racquet 20 has aroughly U-shaped crosssectional configuration, see particularly FIG. 4,defined by a bight 34 and pair of arms 35 extending from opposite endsof said bight in substantially parallel relation. The arms 35 of eachportion 26 have transverse extensions 36 which extend toward each otherand have terminal ends arranged in spaced relation to define a space 37therebetween. The bight 34, arms 35, and extensions 36'of each metalportion 26 have inside surfaces in intimate contact with the elastomericmaterial defining the associated inner portion of the beam 30 stantiallyless than the thickness 41 of the head portion 22 ofthe frame 21.

As seen in FIGS. 1-3, the beam 30 has an inner surface 42 facing towardthe center of the ovaloid head portion 22 and an outer surface 43 whichis recessed inwardly of the metal portions 26 by a distance'indicated at44, see FIG. 4, which is substantially greater than the thickness ofthestrands 32 defining stringing 31 and as illustrated at 45. Thisconstruction assures that the stringing is protected against impactwhich often occurs in the course of play by striking the racquet againstthe surface of the tennis court or may occur by inadvertent striking ofobjects during normal handling of a tennis racquet.

The racquet 20' also has a bridge member or bridge 46 (see FIGS. 1, 5,and 6) which is fixed to the frame 21 using any suitable means such as apair of rivets 47, for example. The bridge 46 cooperates with theapproximately ovaloid head portion 22 to complete the head portion ofthe racquet 20 as an oval. The bridge 46 may be made of any suitablemetallic or n'onmetallic material and in this example such bridge ismade of a resilient elastomeric material and the detailed constructionthereof is such that it provides resiliency in a similar manner as thebeam which is supported between metal portions 26.

The beam 30 provides the sole support for adjoining stringing 31 and inthis example such beam has suitable means therein enabling the stringing31 to be attached in position. In particular, the beam 30 has aplurality of openings each designated by the reference numeral 50 andeach opening 50 is adapted to receive an associated strand 32 of thestringing 31 therethrough with the openings 50 being arrangedsubstantially in a common plane.

The bridge 46 also has a plurality of openings 51 extending therethroughand the openings 51 are also in a common plane. The bridge 46 isinstalled in position by its rivets 47 so that the openings 50 and 51are in substantially the same plane P, see FIG. 2, whereby the stringing31 comprising the striking surface is essentially in one plane with theexception of the normal weave provided in such stringing and asillustrated at 52 in FIG. 3. However, it will be appreciated that eachpair of immediately adjacent openings 50 and 51 may be arrangedsymmetrically 'on opposite sides of the plane P whereby an imaginaryline through each of such pair of openings would be bisected by theplane P. r

The racquet 20 may be made using any suitable tech nique known in theart including the teachings of the patents previously mentioned in thebackground portion of this application. For example, an emptychannel-like elongated structure designated bythe reference numeral 53and made of a metallic material is moved through a filling station54where a suitable elastomeric material (which for simplicity isdesignated by the same reference numeral 30 as the beam 30) is suitablyprovided from a conventional source 58 to a filling head 55 and ejectedfrom a nozzle 56 thereof into an open channel 57 in the elongatedstructure 53 so that a filled structure, designated by the numeral 60,is defined. The filled structure is suitably cured and/or cooled inaccordance with standard practice depending upon the elastomericmaterial 30 employed and the cured and cooled structure is alsodesignated by the reference numeral 60. I The frame 21 is formed usingstructure 60 and using any suitable technique or machine known in theart, such as a conventional tube bending machine. For simplicity, anapparatus and method for forming the structure 60 is illustratedschematically in FIG. 8 and comprises a fixture 61 having a suitabletemplate 62 detachably fixed thereon. The template 62 has aconfiguration such that once the structure 60 is bent or formedtherearound using conventional devices to apply bending forces asindicatedby arrows 63, the structure 60 is bent around the template 62so that even with normal springback of such'structure after forming, thebasic outline of theframe 21 with its ovaloid head portion 22 isdefined.

The member 53 is preferably made by extrusion process and, as will beapparent from FIG. 7 of the drawings, the elongated metallic structure53 is comprised of metal portions 26 joined together as asingle unit byanintegral member 64 extending therebetween and structure 53 may havesuitable weakening lines 65 provided on opposite sides of portion 64.The weakening lines 65 are defined by projections in the extrusion dieused to makestructure 53 and lines 65 enable portion 64 to be readilygrasped with a suitable device and severed from the completed structure60 which is comprised of structure 53. However, it is to be understoodthat the structure 53 need not necessarily have weakening lines 65therein and in this latter instance member 64 is cut or severed fromstructure 53 using any-suitable means. The coplanar spaced openings 50are then provided in the beam 30 whereupon the bridge 46, with openings51 previously formed therein; and handle 25 are attached in position andthe racquet strung with stringing 31 to define theco mpleted racquet 20.

In the above description it is stated that the structure 60 is bentbefore severing the strip 64 therefrom; however, the strip 64(regardless of whether it has weakening lines on opposite sides thereofis preferably severed prior to the bending step illustrated in FIG. 8.Similarly, openings 50 may be provided in the beam 30 prior to formingthe structure 60 about template 62 and after severing of the stripportion 64. In this latter instance. it will be appreciated that theopenings or holes 50 will extend through the beam 30 at the requiredangles of inclination and with the required spacing so that once thestructure 60 is bent about template 62 to define the frame 21, theopenings are arranged at the desired positions assuring the strands 32are precisely positioned relative to each other and to define thestringing 31 essentially as illustrated in FIG. 1.

Another exemplary embodiment of the racquet construction or racquet ofthis invention is illustrated in FIG. 11 of the drawings. The racquetillustrated in FIG. 11 is similar to the racquet 20; therefore, suchracquet will be designated by the reference numeral 20A andrepresentative parts thereof which are similar to corresponding parts ofthe racquet 20 will be designated in the drawings by the same referencenumeral as in the racquet 20 (whether or not such parts are describedhereinafter) followed by the letter designation A and not describedagain in detail. Only those component parts of the racquet 20A ormembers used to make such component parts which are different fromcorresponding parts of the racquet 20 will be designated by a newreference numeral also followed by an associated letter designation anddescribed in detail.

The racquet 20A is comprised ofa frame 21A having an ovaloid headportion 22A and parallel extensions 23A. The head portion 22A is definedby a pair of channel-like metal portions 26A which are held together asa single unit in a bonded manner and spaced in substantially parallelrelation by a beam 30A-made of a resilient elastomeric material and thebeam 30A has an ovaloid configuration which corresponds to the headportion 22A, see FIGS. and 11.

The beam 30A has different thicknesses at various locations along itsovaloid path and as illustrated at 70A, 71A and 72A and each pair ofimmediately adjacent thicknesses is joined by a smooth transitionsection therebetween. Thus, the resiliency of the beam 30A at variouspoints therealong is controlled not only by the resilient characterthereof but also by its different thicknesses. The thicknesses of beam30A at different locations are controlled to assure precision control ofthe resilient character of the stringing 31A at each location takinginto account that at locations where the longest strands 32A areemployed the beam 30A should be stiffest and where the shortest strands32A are employed the beam 30A should have maximum flexibility.

The'frame 21A is preferably made from an elongated structure 73Aillustrated in FIG. 9 which is a roughly U-shaped structure having metalportions 26A interconnected by a strip 74A along weakening lines 75A.The structure 73A is filled with elastomeric material 30A in a similarmanner as illustrated in FIG. 7 for structure 60, stripped of itselongated strip 74A along its weakening lines 75A and then bent orformed as illustrated in FIG. 8. To provide different thicknesses forthe beam 30A comprising the ovaloid head portion 22A, an easily removedexpendable insert 76A may be placed in the elongated Ushaped structureprior to filling with elastomeric material 30A, see FIG. 9, so that oncethe strip 74A is removed the insert 76A is also readily removed todefine the beam 30A having the configuration illustrated in FIG. 11.

However, it will be appreciated that instead of forming theconfiguration of the beam 30A using an insert 76A other techniques maybe employed such as initially defining the beam portion ofa uniformthickness therealong and then suitably machining the desiredconfiguration therein. However, irrespective of the manner in whichdifferent thicknesses are provided at its different locations, the beam30A may have openings 50A formed therein either in its straightcondition or after forming its central portion to define an ovaloidshape in order to allow the stringing 31A to be suitably supportedsolely by the beam 30A in a similar manner as the supporting ofstringing 31 by beam 30 in the racquet 20.

The extensions 23 and 23A may be filled with elastomeric material orsuch extensions need not necessarily be filled with such material. Inaddition, in the extensions 23 and 23A the metal strip 64 and 74Arespectively may be either left in position or suitably severed.Further, in order to achieve precise balance of the overall racquet, thesevering may be achieved over any desired length of the racquetextension stopping at any desired position along such extension fromeither end thereof. 1

Any suitable metallic material may be used to define the metal portionsof the racquet 20 and 20A; however, such racquets are preferably madeusing metallic materials containing aluminum or aluminous materials andthe elongated channel-like structures 53 and 73A are preferably made byextrusion process with the weakened lines of separation defining eachseverable strip being defined in the associated extrusion die.

Any suitable elastomeric material which is capable of providing theperformance desired herein when used in cooperation with the typestringing normally provided with a racquet such as a tennis racquet maybe used to define beams 30 and 30A. Various plastic materials such aspolymers have been used for this purpose and it will be appreciated thatnatural and synthetic rubber compounds may also be used.

While present exemplary embodiments of this invention, and methods ofpracticing the same, have been illustrated and described, it will berecognized that this invention may be otherwise variously embodied andpracticed within the scope of the following claims.

What is claimed is:

l. A racquet construction comprising, a frame having an ovaloid headportion terminating in a pair of closely spaced parallel extensions,said head portion being defined by a pair of spaced metal portionshaving inside surfaces which face generally toward each other, and abeam having a peripheral outline which corresponds substantially to theoutline of said metal portions and being attached therebetween, saidbeam being made of a single body of one particular resilient elastomericmaterial which provides the sole support for adjoining stringingextending thereacross, said beam holding said metal portions insubstantially parallel relation and when viewed at any cross sectionalong its length is attached at its opposite end portions only againstsaid inside surfaces while being unsupported between said end portions,said beam having different controlled radial thicknesses at differentlocations about its periphery, said different controlled radialthicknesses serving to control the resiliency of said beam and henceproviding precision control of the resilient character of saidstringing.

2. A racquet construction comprising, a frame having an ovaloid headportion terminating in a pair of closely spaced parallel extensions,said head portion being defined by a pair of spaced metal portionshaving inside surfaces which face generally toward each other. and abeam having a peripheral outline which corresponds substantially to theoutline of said metal portions and being attached therebetween, saidbeam being made of a single body of one particular resilient elastomericmaterial which provides the sole support for adjoining stringingextending thereacross, said beam holding said metal portions insubstantially parallel relation and when viewed at any cross sectionalong its length is attached at its opposite end portions only againstsaid inside surfaces while being unsupported between said end portions,each of said pair of spaced metal portions having a roughly U-shapedcross-sectional configuration defined by a bight and a pair of parallellegs extending from said bight, said metal portions being arranged withtheir outwardly extending legs extending toward each other and receivingsaid beam in nested relation therewithin and said inside surfacesinclude the inside surfaces of said bight and parallel legs.

3. A racquet construction comprising, a frame having an approximatelyovaloid head portion terminating in a pair of closely spaced parallelextensions, said head portion being defined by a pair of spaced metalportions having inside surfaces which face generally toward each other,said metal portions being held together by a single body of oneparticular resilient elastomeric material which extends thereacross anddefines a supporting beam for stringing provided as a part of saidracquet and when viewed'at any cross section along its length saidbeam-is attached at its opposite end portions only against said insidesurfaces while being unsupported between said end portions, and supportmeans in said elastomeric material providing the sole support for saidstringing, said support means comprising a plurality of substantiallycoplanar openings extending through said elastomeric material with saidopenings being adapted to receive individual strands of said stringingtherethrough to enable attaching said stringing solely against saidelastomeric material, said metal portions each having a channel-likeconfiguration.

4. A racquet construction comprising, a frame having an approximatelyovaloid head portion terminating in a pair of closely spaced parallelextensions, said head portion being defined by a pair of spaced metalportions having inside surfaces which face generally toward each other,said metal portions being held together by a single body of oneparticular resilient elastomeric material which extends thereacross anddefines a supporting beam for stringing provided as a part of saidracquet and when viewed at any cross section along its length said beamis attached at its opposite end portions only against said insidesurfaces while being unsupported between said end portions, and supportmeans in said elastomeric material providing the sole support for saidstringing, said support means comprising a plurality of substantiallycoplanar openings extending through said elastomeric material with saidopenings being adapted to receive individual strands of said stringingtherethrough to enable attaching said stringingsolely against saidelastomeric material, said metal portions each having a roughly U-shapedcrosssectional configuration defined by a bight and a pair of parallelarms with said parallel arms having transverse extensions which extendtoward each other and have terminal ends arranged in spaced relation todefine a space therebetween, said bight, arms, and extensions havinginsidesurfaces which define said first-named inside surfaces and are inintimate contact with the elastomeric material and said elastomericmaterial extending through said space having a thickness which issubstantially less than the thickness of said frame.

5. A racquet construction as set forth in claim 4 in which saidelastomeric material has an inner and an outer'surface, said outersurface being recessed inwardly of an outer surface of said metalportions by a distance which is substantially greater than the thicknessof said stringing.

1. A racquet construction comprising, a frame having an ovaloid headportion terminating in a pair of closely spaced parallel extensions,said head portion being defined by a pair of spaced metal portionshaving inside surfaces which face generally toward each other, and abeam having a peripheral outline which corresponds substantially to theoutline of said metal portions and being attached therebetween, saidbeam being made of a single body of one particular resilient elastomericmaterial which provides the sole support for adjoining stringingextending thereacross, said beam holding said metal portions insubstantially parallel relation and when viewed at any cross sectionalong its length is attached at its opposite end portions only againstsaid inside surfaces while being unsupported between said end portions,said beam having different controlled radial thicknesses at differentlocations about its periphery, said different controlled radialthicknesses serving to control the resiliency of said beam and henceproviding precision control of the resilient character of saidstringing.
 2. A racquet construction comprising, a frame having anovaloid head portion terminating in a pair of closely spaced parallelextensions, said head portion being defined by a pair of spaced metalportions having inside surfaces which face generally toward each other,and a beam having a peripheral outline which corresponds substantiallyto the outline of said metal portions and being attached therebetween,said beam being made of a single body of one particular resilientelastomeric material which provides the sole support for adjoiningstringing extending thereacross, said beam holding said metal portionsin substantially parallel relation and when viewed at any cross sectionalong its length is attached at its opposite end portions only againstsaid inside surfaces while being unsupported between said end portions,each of said pair of spaced metal portions having a roughly U-shapedcross-sectional configuration defined by a bight and a pair of parallellegs extending from said bight, said metal portions being arranged withtheir outwardly extending legs extending toward each other and receivingsaid beam in nested relation therewithin and said inside surfacesinclude the inside surfaces of said bight and parallel legs.
 3. Aracquet construction comprising, a frame having an approximately ovaloidhead portion terminating in a pair of closely spaced parallelextensions, said head portion being defined by a pair of spaced metalportions having inside surfaces which face generally toward each other,said metal portions being held together by a single body of oneparticular resilient elastomeric material which extends thereacross anddefines a supporting beam for stringing provided as a part of saidracquet and when viewed at any cross section along its length said beamis attached at its opposite end portions only against said insidesurfaces while being unsupported between said end portions, and supportmeans in said elastomeric material providing the sole support for saidstringing, said support means comprising a plurality of substantiallycoplanar openings extending through said elastomeric material with saidopenings being adapted to receive individual strands of said stringingtherethrough to enable attaching said stringing solely against saidelastomeric material, said metal portions each having a channel-likeconfiguration.
 4. A racquet construction comprising, a frame having anapproximately ovaloid head portion terminating in a pair of closelyspaced parallel extensions, said head portion being defined by a pair ofspaced metal portions having inside surfaces which face generally towardeach other, said metal portions being held together by a single body ofone particular resilient elastomeric material which extends thereacrossand defines a supporting beam for stringing proviDed as a part of saidracquet and when viewed at any cross section along its length said beamis attached at its opposite end portions only against said insidesurfaces while being unsupported between said end portions, and supportmeans in said elastomeric material providing the sole support for saidstringing, said support means comprising a plurality of substantiallycoplanar openings extending through said elastomeric material with saidopenings being adapted to receive individual strands of said stringingtherethrough to enable attaching said stringing solely against saidelastomeric material, said metal portions each having a roughly U-shapedcross-sectional configuration defined by a bight and a pair of parallelarms with said parallel arms having transverse extensions which extendtoward each other and have terminal ends arranged in spaced relation todefine a space therebetween, said bight, arms, and extensions havinginside surfaces which define said first-named inside surfaces and are inintimate contact with the elastomeric material and said elastomericmaterial extending through said space having a thickness which issubstantially less than the thickness of said frame.
 5. A racquetconstruction as set forth in claim 4 in which said elastomeric materialhas an inner and an outer surface, said outer surface being recessedinwardly of an outer surface of said metal portions by a distance whichis substantially greater than the thickness of said stringing.